The invention relates to an improved method and apparatus for calibrating probe cards to ensure that appropriate overdriven probe needles are in proper alignment with bonding pads of an integrated circuit chip to be "probe tested", and more particularly to an inverted alignment station for performing such calibrating.
In the integrated circuit manufacturing industry each semiconductor wafer may include hundreds of integrated circuit die (i.e., chips), and it is necessary to "probe test" each die before the wafer is cut into the individual integrated circuit die which then are packaged. Such testing often requires most bonding pads to have electrical contact to a tester. To accomplish the probe testing, it is conventional to provide "probe cards" that support a plurality of probe needles, the tips of which must provide electrical contact with corresponding bonding pads of the die under test (DUT). The shank of a probe needle is typically 5 to 10 mils in diameter, and the wafer to be probed is supported on a wafer chuck. Typically, the probe needles are inclined relative to the bonding pads. After alignment of the probe needles with the corresponding bonding pads of the integrated circuit die has been accomplished, the wafer chuck is raised through an approximately 3 mil "over-travel distance" past the point at which the probe tips first contact the pads so that the typically inclined probe needles slide or "scrub" on the aluminum bonding pads of the die to allow good mechanical and electrical contact thereto.
In the course of manufacturing the probe cards, it is necessary to align the probe needles to a "mask" having imprinted thereon "dots" or "targets", the locations of which correspond precisely to the locations of the bonding pads on the die to be probed. As mentioned above, the probe needles are "overdriven" approximately 3 mils during probe testing of an integrated circuit die, so it is necessary to provide the same 3 mils of "overdrive" during "probe needle alignment" with the dots on the mask. Probe needle alignment usually has been performed on a device called an "alignment station". The above mentioned "mask" is located therein with the dots facing upward on a vertically moveable chuck. The probe card to be aligned is mounted securely in the alignment station, with the probe needles pointing downward and as closely aligned as possible with the corresponding dots on the mask. Skilled operators then manipulate suitable tweezers to adjust the probe needles. To accomplish this task, the operator views the needles through a microscope. When the chuck is raised to provide the 3 mil overdrive, the operator identifies needles which need to be bent slightly to be properly aligned with their corresponding dots on the mask. The mask then is lowered so it no longer contacts the needles. The operator then manipulates the tweezers to bend the misaligned needle(s), again raises the chuck to the overdriven position, and re-observes the alignment of the adjusted needles with its corresponding pad on the mask. This procedure is repeated until all needles are properly aligned with the corresponding dots on the mask in the overdriven position. At that point the probe card is ready for use in testing a wafer.
However, the above technique does not allow adequate access to probe needles for the high density, complex probe cards which are needed to test multi-DUT arrays or some of the more complex integrated circuits now being manufactured. Furthermore, the task of aligning probe needles is very taxing to the operators, because of the great precision required in manipulating the tweezers while simultaneously straining to view the needles and tweezers through the microscope. For multi-layer probe needle assemblies, the operator needs to move the upper probe needles out of the way in order to gain access to allow alignment of the lower probe needles. This is very taxing upon the abilities of an operator.
It would be highly desirable to provide an improved probe needle alignment device and system which allows better access for tools such as tweezers to align probe needles with corresponding dots on a mask, allows more accurate alignment of probe needles prior to use, and which also avoids the operator fatigue usually associated with probe needle alignment procedures.